1. Technical Field of the Present Invention
The present invention generally relates to programmable active terminations, and more specifically to programmable active terminations of Input/Output devices.
2. Background of the Present Invention
The electronic industry is in a state of evolution spurred by the recent changes in technology which have allowed greater functionality in smaller devices. This has resulted in the explosion of new found uses for such small devices (e.g. medical, monitoring etc.), as well as greater functionality in increasingly smaller electronic devices.
The evolution has caused electronic devices to become an inseparable part of our society. Consumers are now buying and demanding electronic devices which are smaller, more powerful, and faster at unprecedented rates. These demands are constantly driving the electronic industry to exceed limitations which were previously considered unsurpassable.
One such area ripe for improvement is how various electronic devices communicate with one another. For example, the communication between the memory and cpu of a computer. This communication is accomplished using a system data bus. The primary concerns of this type of communication are signal propagation delay and capacitive loading. Propagation delay is minimized by placing the memory as close to the cpu as possible. Capacitive loading is minimized by using point-to-point networks. As the speed of the system data bus approaches one Giga Hertz and beyond, the data transfers must be point-to-point terminated. The point-to-point termination is accomplished by terminating each signal trace to a reference voltage via the use of resistors (xe2x80x9cterminating resistorsxe2x80x9d).
The implementation of the point-to-point termination while minimizing signal propagation delay and capacitive loading has resulted in requiring the terminating resistors to reside on the chip itself (xe2x80x9con-chipxe2x80x9d). Since the termination resistors are critical to both the timing and integrity of transmitted signals, they must be highly accurate (i.e. resistance values will not vary when exposed to changes in process and/or temperature). Unfortunately, the terminating resistors also require a considerable amount of space and consume a significant amount of Direct Current (DC) power.
It would therefore be a distinct advantage to have a method and apparatus for providing on-chip termination resistance that would be highly accurate, occupy less space, and consume less DC current than current terminating resistors. The present invention provides such a method and apparatus.
The present invention is a method and apparatus for providing programmable active termination of transmission lines.